This invention is an improvement to the switching amplifier disclosed in my U.S. Pat. Nos. 4,087,732 and 4,140,956. This switching amplifier is used to drive stepping motors and is related generally to switching amplifiers for inductive loads.
Stepping motors are specialized synchronous motors designed to be driven over a wide range of speeds including being stopped. The low-frequency energization of stepping motors must limit the motor current to keep the motor from incinerating. The prior art contains many approaches to limiting the motor current. Of these, switching amplifiers provide the greatest performance with the best efficiency. The switching amplifier disclosed herein is a single supply voltage variety and not the dual voltage type which uses the higher voltage to create the rapid current rise needed for high speed operation and a lower voltage to maintain the motor current without overheating. More specifically, the amplifier disclosed herein attempts to control the motor current between two thresholds, whose values are the amplifier input offset by an internally generated hysteresis signal. It is important to compare these thresholds against accurate representations of the motor current so that the amplifier is more nearly linear.